A macabre parasitic wasp turns social spiders into "zombies"

By far, the largest number of wasps (over 100,000 species) are parasitoids that lay their eggs in or on the caterpillars of other insect species. This makes them great pest control facilities and farmers love them because they cause little or no crop injury. In fact, some farmers buy parasitic wasps to control insects in their fields.

However, some wasps have pushed their role of freelancer to a new level of morbidity. For example, bile wasps (Bbadettia pallida) pierce tiny holes in the oaks to eat them from the inside. Wasps also use these tunnels, called "crypts", as shelters and hatcheries. When the young bile wasps are ready, they nibble through the woody stems and emerge in adulthood. Another type of wasp, known as Euderus, catch this behavior and lay eggs in these holes, even if they are occupied by developing bile wasps. In fact, it's the idea. Once they hatch, the Euderus wasps will make their way to freedom, eating through the poor wasp and emerging through the head! The biliary wasp can not escape because the hole is large enough to support the development of the Euderus hump and wasp, but not large enough to leave room for the wasp's head.

The strategy of the wasp, for example, is to "zombie" the badroaches and inject them with larvae. The infected badroach begins to groom intensively, loses its survival instinct and normal responses, and becomes a reluctant host and breakfast for the wasp offspring. The wasp offspring will eat the organs of the badroach so that the insect stays alive longer, increasing the chances of survival of the offspring. This behavior is widespread because of the fact that badroaches had to adapt using "karate kicks" to protect themselves against the macabre intruder.

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Researchers at the University of British Columbia recently discovered another zombie wasp during a study of the tropical rainforests of Ecuador. The wasp targets one of the 25 known social spider species in the world. Anelosimus eximius Spiders live together in large colonies, where they hunt together and share parental responsibilities.

These spiders rarely move away from their basket-shaped nest – unless they have encountered the Zatypota wasp. Philippe Fernandez-Fournier, a former graduate student at the University of British Columbia and lead author of the new study, was surprised by the strange behavior of some A. eximius spiders, that he saw wandering a few feet from the nest. The individuals were spinning closed canvases of dense silk and pieces of foliage, called "cocoon cloths". When some of these structures were collected and examined in the laboratory, much to the surprise of all, the researchers discovered that they covered a wasp.

"Wasps manipulating the behavior of spiders have already been observed, but not at such a complex level," said Philippe Fernandez-Fournier, lead author of the study and former master's student at the Zoology Department of the University of Montreal. University of British Columbia. "Not only does this wasp target a species of social spider, but it makes her leave her colony, which she rarely does … These wasps are very elegant and graceful, but then they make the most brutal thing. "

Female wasps first lay an egg on the spider's abdomen, whose larvae hatch and then attaches to the host. The larva feeds on the hemolymph resembling spider blood while it slowly picks up from its body. At one point, the zombified individual starts to leave the colony and spins a cocoon for the larva. After consuming the remaining nutrients, the larvae enter the cocoon shaped by its slave arachnid and emerge fully developed until 11 days later.

"But this change in behavior is so hardcore," said Samantha Straus, co-author of the study published in Ecological Entomology and a doctoral student at UBC, said in a statement. "The wasp completely diverts the spider's behavior and brain and makes it do something it would never do, like leaving its nest and turning on a completely different structure. It's very dangerous for these little spiders.

Researchers believe that wasps inject spiders with hormones that make them feel like they are living in a different phase of life or dispelling them from the colony.

"We think wasps are targeting these social spiders because they provide a large stable host colony and a source of food," Straus said. "We also found that the larger the spider colony, the more likely it was that these wasps would target it."

In the future, researchers plan to return to Ecuador, where they wish to further study the same spider colonies and parasitic wasps.

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